The present invention relates generally to thermocouple devices, and particularly to a thermocouple device having pointed, thermocouple elements providing a unitary pointed end capable of repeated engagements with objects to be measured for their temperature.
In measuring the temperature of hot metal ingots, for example, thermocouple elements of temperature measuring devices are preferably pointed and disposed directly against the surfaces of the ingots with a force sufficient to penetrate any oxide layer on the ingots. It can be appreciated that repeated engagements of such ingots or other metal objects will tend to blunt and bend the pointed elements, with the result of unreliable, inaccurate temperature readings and/or frequent replacement of the elements, unless such elements are sufficiently rugged or protected by rugged, heat resistant structures. Yet, attempts to ruggedize and to increase the useful life of thermocouple elements have heretofore resulted in structures that tend to reduce the response time and accuracy of the thermocouples because of the increase in the mass and heat sinking effect of such structures.
For example, the response and accuracy of a thermocouple junction located in the pointed end of a 3/8 inch diameter, approximately 1/16 inch thick, steel probe is very poor, the increase in the temperature of the junction being slow and gradual after the steel probe is placed in contact with the object under test. The junction of this device required two and a half (21/2) minutes to reach its final temperature reading; the object measured in this test was a 3/16 inch thick aluminum plate held at 600.degree. F.
In an effort to extend the life of a two point thermocouple device, the pointed ends of the thermocouple elements of the device were coated with a layer of chrome, and the elements mounted approximately 1 inch apart in parallel relation in an insulating handle. In testing this device, using the above, 600.degree. F, aluminum plate, the final temperature of the thermocouple elements was not reached until 1.5 minutes had elapsed. Even though response time and accuracy of this device indicated improvement over the steel tube probe, it was not sufficiently accurate for production processes, in which ingots, for example, are being continuously heated and directed to extrusion presses, the temperature of each ingot being preferably measured before it enters the press.
In addition, it has been found that with hand-held devices having two thermocouple elements spaced apart a distance of about an inch or so, it is difficult to obtain repeatable, accurate, temperature measurements unless the elements engage the object being measured in a direction substantially perpendicular to the object, i.e. two point thermocouple elements tend to be sensitive to the angle of application and the amount of the pressure at which the elements are applied. It can be appreciated that it is difficult, if not impossible, for a workman or workmen taking temperature readings to consistently apply such thermocouple elements at the proper angle and pressure.
Bare thermocouple elements made of flat, planar stock and fused together along opposed bevelled edges of the stock to form an elongated edge, such as shown in U.S. Pat. No. 2,978,527 to Forde, again present a substantial mass and heat sink to be heated by the object under test, so that response and accuracy of such devices are inadequate in terms of the objectives and advantages of the present disclosure. This was found to be true even with pointed elements made from round stock and fused together at their thermocouple ends. Several of such devices were made and tested, and found to have slow response times, which were probably due to the mass of the fused material.